The present invention relates to a control system for controlling movement of a tool carried by a machine and, more specifically, to a control system for controlling movement of individual hydraulically moveable ends of a tool which carries laser receivers, even when one of the receivers does not receive the transmitted plane of reference light.
In concrete paving operations, after concrete is poured, it is commonly finished by drawing a tool, such as a screed head, over the surface of the concrete. This smooths the surface of the concrete before it cures. In asphalt paving operations, after asphalt is laid, it is commonly leveled to a desired depth by drawing a tool, such as also a screed head of a paver, over the surface of the contour. Finally, in grading operations, a surface is graded to a desired depth by drawing a tool, such as a blade of a grader, over the surface of the contour. Thus, although the physical configurations of the types of screed heads and the grader""s blade are not identical, the functions of these tools are analogous.
Typically, hydraulic cylinders connected to each end of the tool of the machine are used to raise and lower the ends of the tool independently. It has been common to determine the elevational positions of the ends of the tool by using a laser transmitter which provides a rotating beam of laser light, effectively producing a reference plane. The raising and lowering of the tool are controlled by a control system that has a predetermined desired eleveational position for the surface.
A pair of laser receivers, one receiver mounted at each end of the tool on an associated mast for vertical movement with the tool, detects the reference plane and the relative elevation of the ends of the tool with respect to the reference plane. A control system of the machine then actuates hydraulic valves to supply fluid to the hydraulic cylinders in response to these detected levels. As a result, the elevation of each end of the tool can be precisely controlled. Each of the receivers provides elevational feedback to drive the hydraulics controlling the elevation of the end of the tool with which it is associated.
Prior to operating a machine of this type, a machine setup operation has been performed. This has been accomplished by first setting the laser transmitter in a location that will minimize the occurrence of beam blockage from any surrounding obstructions. The operator then uses a grade rod with a handheld beam detector to transfer the sight benchmark to the tool. The typical method of setting up a screed machine has been to place the grade rod on a rod platform provided specifically for this purpose on the left side of the screed head. The laser receiver on the left side of the screed head is then adjusted up or down(causing the screed head to move up or down) until the hand-held laser receiver indicates that an on-grade position has been reached. At this point, the elevation of the left laser receiver is locked and the procedure repeated on the right side.
The disadvantage of this method is that very small setup errors at opposite ends of the screed head become readily apparent when the screed machine is used. If the operator is not careful, it is easy for one side of the screed head to be xe2x85x9 inch lower than the correct elevation and the other side of the screed head to be xe2x85x9 inch higher than the correct elevation. This would result in a total deviation from one end to the other of xc2xc inch. Since each pass of the screed head over the surface of the concrete causes areas that are smoothed by the screed head at one end to abut other areas that are smoothed by the screed head at its opposite end, such deviations would be very apparent, as the final floor surface has a sawtooth grade with a series of xc2xc inch discontinuities.
It is seen, therefore, that there is a need for a control system and method for controlling movement of individually hydraulically moveable ends of a tool, such as a screed head, to maintain a selected elevational position between each end of the tool and an elevation reference in which the setup of the control system is facilitated to reduce errors.
This need is met by the method the present invention for setup of a control system for a machine having a tool with hydraulically moveable ends, such as a screed head. The elevational positions of the ends of the tool and the orientation of the tool along its length from one end to the other being controlled to be on grade during operation in relation to a reference detected by elevation receivers attached to the ends of the tool. According to this method, the on grade elevational position of the first end of the tool with respect to the reference is selected, and the first end of the tool moved to the desired elevational position with the elevation receiver at the first end detecting the reference. The on grade orientation of the tool along its length from one end to the other is selected, and the second end of the tool moved until the on grade orientation of the tool along its length is sensed. The reference is detected with the elevation receiver at the second end of the tool, and the detected positions of the reference at the first and second ends of the tool are stored as on grade positions.
The step of moving the second end of the tool until the on grade orientation of the tool along its length is sensed may include the step of sensing the orientation of the tool using an inclinometer. The inclinometer is preferably permanently attached to the tool.
The elevation receivers are preferably light detectors and the reference is preferably a rotating beam of light. Even more preferably, the elevation receivers may be laser light detectors and the reference is a rotating beam of laser light.
Other objects, features and advantages will appear more fully in the course of the following discussion.